The present invention relates to a vehicle driving force control, and more particularly to a driving force control system for a vehicle powertrain including a prime mover in the form of an internal combustion engine and a transmission in the form of a continuously variable transmission (CVT).
The term xe2x80x9cstandard running resistancexe2x80x9d is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term xe2x80x9crunning resistancexe2x80x9d is herein used to mean any force that opposes the motion of an automotive vehicle, which is driven to keep on rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term xe2x80x9cacceleration resistancexe2x80x9d is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term xe2x80x9cgradient resistancexe2x80x9d is used to mean this increment or difference in running resistance.
JP-A 62-110535 and JP-A 6-17684 disclose vehicular driving force control systems. According to JP-A 62-110535, a target horsepower is determined in response to accelerator position and vehicle speed. The target horsepower is used to determine a target CVT input speed. The target horsepower cooperates with the actual CVT input speed to determine a target engine torque. The target engine torque is used to determine a target throttle position of the engine.
According to JP-A 6-17684, standard target acceleration is determined in response to accelerator position, and actual acceleration is determined by differentiating a measure of a vehicle speed sensor. A deviation between them is integrated and then added to the standard target acceleration. The result is multiplied with a predetermined vehicle weight to give a target driving torque. The target driving torque is used in engine torque control and also in transmission ratio control.
A need remains to improve a driving force control system to carry out driving force correction without deteriorating the vehicle""s operator drive comfort.
An object of the present invention is to provide a driving force control system to meet such need.
FIGS. 11 (A), 11 (B) and 11 (C) illustrate the case where the same driving force correction generated in response to the running resistance increment is added to an ordinary target driving force. In this case, the ratio is held at the largest ratio Lo before the vehicle""s operator depression of the accelerator pedal increases to or near the fully depressed position. Thus, the engine speed increases during operation at or near the fully depressed position of the accelerator pedal. The present invention has avoided the occurrence of such exemplified case.
According to one aspect of the present invention, there is provided a driving force control system for an automotive vehicle powertrain including a prime mover and a continuously variable transmission (CVT), the prime mover being operable to accomplish a target output torque, the CVT being operable to alter a CVT ratio to accomplish a target ratio, the driving force control system comprising:
an accelerator pedal sensor to detect the vehicle""s operator depression of an accelerator pedal of the vehicle;
a vehicle speed sensor to detect a vehicle speed of the vehicle; and
a power train controller that is operative
to determine an ordinary target driving force in response to the detected vehicle""s operator depression of the accelerator pedal and the detected vehicle speed,
to determine a driving force correction,
to determine a first corrected target driving force after correcting the determined ordinary target driving force in response to the determined driving force correction,
to determine a second corrected target driving force after correcting the determined ordinary target driving force in response to the determined driving force correction,
said first and second corrected target driving forces being different from each other, and
to determine the target output torque and the target ratio in response to the determined corrected first and second target driving forces, respectively.